It is known to employ rotating rectifier assemblies in generators, such as high speed generators utilized in aircraft. The use of rotating rectifier assemblies permits the elimination of brushes which frequently require maintenance and/or replacement.
A typical brushless generator has three distinct generating systems, including a main generator, an exciter and a permanent magnet generator. The permanent magnet generator includes permanent magnets for establishing a magnetic field which is employed to induce a current field in a set of windings. This induced current is in turn employed to generate a magnetic field in the exciter; and this magnetic field in turn is employed to induce an even higher level of current, typically three phase alternating, which is then employed to generate a magnetic field for the main generator.
In order to avoid the use of brushes, it is necessary that the magnetic field and the main generator be in the rotor so that the output of the system can be taken from the stator of the main generator. To generate a suitable magnetic field in the rotor, it is necessary to utilize direct current, as opposed to alternating current. Since the output of the exciter is an alternating current, this current must rectified to direct current. A rectifier assembly is used for this purpose. In order to avoid resort to brushes, it is necessary that the rectifier assembly interconnecting the exciter and the main generator field winding be carried by the rotor of the generator. U.S. Pat. Nos. 4,570,094; 4,603,344 and 4,628,219 disclose examples of known rotating rectifier assemblies.
Rotating rectifier assemblies carried in a rotor of a generator are subjected to high centrifugal loading so that much care must be taken to assure that the components of the rectifier are adequately supported against such forces. For example, some rectifiers must be designed to withstand speeds as high as 30,000 rpm. The diode semiconductor devices used in the rectifier assemblies also dissipate power in the form heat during their use. Without proper attention to cooling, the diode semiconductor devices will fail. In the known rotating rectifier assemblies of the aforementioned U.S. patents, the diode semiconductor devices and other assembly components are compressed in a direction along the axis of rotation of the rectifier assembly for maintaining good electrical contact and for maintaining contact of the diode wafers with adjacent heat sinks, the cooling of the diode semiconductor devices being accomplished by circulation of a coolant in contact with the heat sinks.
In aircraft generating systems, in addition to the usual reliability concerns, size and weight restrictions are significant. The compactness, or lack thereof, of the rotor will dictate certain bearing and housing size selections, and thus affect the weight of the system. Since the rotating rectifier assembly forms part of the rotor and therefore influences its size, every effort is made to minimize its size and weight.